In-Cell Touch Display Driver IC Pin Count Reduction
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Solution Overview
Problem
The high pin count in Touch Display Driver Integration (TDDI) chips for large LCD displays increases packaging and testing costs due to the need for numerous touch sensing channels, which existing methods have not adequately addressed.
Innovation Solution
The design incorporates an active in-cell sub-pixel with a Display_Touch signal that switches between display-driving and touch-sensing modes, using a thin film transistor, liquid crystal capacitor, storage capacitor, and active switching element to multiplex data lines for both functions, reducing the pin count by sharing resources between display driving and touch sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If additional touch sensing channels are integrated into a display driver IC to enable in-cell self-capacitive touch sensing, then touch sensing functionality is achieved, but the number of pads increases significantly, increasing packaging and testing costs
Solution Approach 1:
The data lines are designed to serve dual purposes: functioning as display data lines during display mode and as touch sensing lines during touch sensing mode. This multi-functionality is achieved through an active switching element that reconfigures the connection of the liquid crystal capacitor's first terminal between the common electrode (display mode) and the data line (touch sensing mode), allowing the same physical lines to perform both display and touch sensing functions without requiring separate dedicated touch sensing channels
Solution Approach 2:
The system dynamically reconfigures the circuit topology based on operating mode. During display mode, the active switching element connects the liquid crystal capacitor to the common electrode for normal display operation. During touch sensing mode, the switching element is controlled to connect the liquid crystal capacitor to the data line, transforming it into a touch sensing channel. This dynamic reconfiguration allows the hardware to adapt its function based on operational requirements
2Area of stationary object
If the number of touch sensing channels is increased to support larger display sizes, then touch sensing coverage is improved, but packaging and testing costs increase due to more pads
Solution Approach 1:
The invention enables each data line to function as both a display data line and a touch sensing line. For larger displays requiring more touch sensing channels, the existing data lines are reused for touch sensing purposes through the active switching mechanism, eliminating the need to add separate touch sensing lines that would require additional pads and increase manufacturing complexity
Solution Approach 2:
The display driving function and touch sensing function are merged into a single integrated system using the same physical infrastructure (data lines). The active switching element enables seamless switching between these two functions, combining what would traditionally require separate hardware resources into a unified architecture that reduces overall pad count and manufacturing cost
Data Source
AI summary
Embodiments of an active in-cell sub-pixel in an LCD panel are provided for time multiplexing image display and touch sensing so as to reduce pin counts required in display driver integrated circuits. In one embodiment, the sub-pixel comprises a liquid crystal capacitor, a storage capacitor and an active switching element. One terminal of the liquid crystal capacitor is connectable to a data line via a thin film transistor switch. The active switching element is connected to another terminal of the liquid crystal capacitor, and is externally controllable. In one configuration, the active switching element connects the liquid crystal capacitor to a second common electrode of the panel, causing the display-driving mode to be turned on. In another configuration, the active switching element connects the liquid crystal capacitor to the data line, causing the touch-sensing mode to be turned on.